The present invention relates to an automatic sewing machine, in which relative movement in a workpiece and a sewing head is controlled by a computer receiving a program according to a predetermined contour to be stitched. In particular, the present invention relates to a method and device for increasing the rate of production and the reliability for operating such sewing machines.
In such CNC-controlled sewing automats an individual sewing contour is given by a program stored on a data carrier, e.g. a punched tape or an EPROM-cassette into the computer. The contour represents the path of the needle with respect to the workpiece. The contour is determined by perpendicular coordinates of some significant points, which form the variables of an algorithm applied for figuring all required values of a contour by using linear or square interpolation. Thus, by the input of such siginificant points the basic profile of the contour is determined. Furthermore, it is required that the workpiece clamp is formed with a profile that is matched to the contour controlled by the computer. In case of implementing a workpiece clamp that does not fit to the programmed contour, the sewing head of the sewing automat or the workpiece clamp and, under particular circumstances, the drive motors will be damaged. Therefore, it is necessary to check the matching of an inserted workpiece clamp with the computer-controlled contour prior to initiating a sewing process. As this checking procedure should be performed in a minimum of time, on one hand, and since misoperation on the other hand must be eliminated, it has proved necessary to automatically perform this control procedure prior to the sewing process and to carry out this control without action from the operator.
Moreover, besides the input of the significant points determining the basic profile of the contour, the algorithm considers a further variable corresponding to a size adjustment of the workpiece clamp. The workpiece clamp is formed for a size adjustment so that a left and a right half of the workpiece clamp is relatively adjustable to each other and in parallel to one coordinate axis. Due to this adjustment the program put into the computer must be modified correspondingly. As the size adjustment depends on the actual size of the workpiece, a stepless adjustment is desired to a great extent so that it is required to correspondingly alter the input of size information for the computer in a stepless manner.
In a known automatic sewing machine there are four microswitches provided which cooperate with exchangeably contoured workpiece clamps. After the installation of a certain workpiece clamp a characterizing shift status is indicated by the switches which are being read and compared by the computer with the loaded program. Only after this checking procedure can the sewing process be initiated as far as both the loaded program and the workpiece clamp show an associated contour. Indeed, by this known application of a number of switches for identifying a workpiece clamp, damaging of the sewing machine caused by mis-operation is eliminated. However, it is necessary to install a plurality of switches including wiring, which is costly. Due to the physical extension of such switches the number of identification codes is limited to the number of sixteen, for four switches.
From the German laid-open document No. 29 38 064 or the corresponding U.S. Pat. No. 4,312,283 there is known a sewing machine installed with a workpiece receiving device composed of two parts which are adjustably arranged with respect to each other for receiving workpieces of different sizes. According to this publication the computer controlling the sewing machine is operably connected to a stepless working encoder connected to the both parts of the workpiece clamp so as to transmit corresponding electrical information in an automatic manner to the computer. Such an encoder, which is connected by means of a rack and pinion to the two size-adjustable parts of the workpiece clamp, is expensive and limited with respect to reliable operation. Furthermore, under particular circumstances, the zero setting of such an encoder is required prior to the operation of the automatic sewing machine.
It is therefore the main object of the present invention to provide a method for assuring safe operation of an automatic sewing device with simultaneous increase in the production rate.
Another object of this invention is to provide a method of the aforesaid kind, in which already-existing components are employed for a checking procedure.
Still another object of this invention is to provide a method with a large number of codes for identification.
A further object of the present invention is to provide sewing apparatus for carrying out the afore-described method using a reduced number of components, thereby increasing reliability and reducing costs for manufacture.
Still a further object of this invention is to provide sewing apparatus of the aforesaid character, in which space consuming elements used for such a checking procedure are eliminated.